Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.96	13.558%	$39.6999	$39.70	$39.70	$39.70
Purchase #2	$86.64	12.509%	$97.4778	$97.48	$97.50	$97.50
Purchase #3	$217.30	13.660%	$246.9832	$246.98	$247.00	$247.00
Purchase #4	$88.89	13.444%	$100.8404	$100.84	$100.85	$100.80
Purchase #5	$250.51	5.124%	$263.3461	$263.35	$263.35	$263.30
Purchase #6	$84.83	6.739%	$90.5467	$90.55	$90.55	$90.50
Purchase #7	$64.50	10.400%	$71.208	$71.21	$71.20	$71.20
7 purchase totals =	$827.63		$910.1021	$910.11	$910.15	$910.00